| wf2.lean:3:8-3:17: error: failed to prove termination, possible solutions: | |
| - Use `have`-expressions to prove the remaining goals | |
| - Use `termination_by` to specify a different well-founded relation | |
| - Use `decreasing_by` to specify your own tactic for discharging this kind of goal | |
| x y : Nat | |
| h✝ : x < y | |
| ⊢ x - 1 < x |